Precipitation hardening, aka age hardening in several common metal alloys requires a two step
heat treatment to develop the desired strength and hardness.
In the first step, the “solution treatment” or “solution anneal”; the alloy is heated to a
temperature at which the alloy constituents form a solid solution of the elements. Once the
desired distribution of elements is achieved, the alloy is cooled at a rate fast enough to inhibit
diffusion and suppress the formation of “precipitates”.
In the second step,the “precipitation” or “aging” treatment; the alloy is held at a temperature
where the rate of diffusion promotes the formation of the precipitates in the structure and results
in increased hardness and strength.
Age hardening alloys are found in steels, stainless steels, nickel alloys, and among aluminum
alloys.